1. Field of the Invention
The present invention relates to a drive circuit for an emitting device that emits at least light or electrons, such as a light emitting diode, a semiconductor laser, an electroluminescence device, or an electron-emitting device.
2. Description of the Related Art
If an emitting device and a drive circuit are connected to each other by a wiring member such as a flexible wiring board and the emitting device is driven, a voltage drop is caused in a wiring member by resistance in the wiring member and a current flowing through the wiring member and the effective drive voltage actually applied to the emitting device might become lower than the output drive voltage of the drive circuit.
FIG. 8 is a diagram schematically showing a matrix display panel 100 formed by combining surface conduction electron-emitting devices 101 and phosphors (not illustrated).
As resistors that affect the effective drive voltage for the electron-emitting devices 101, wiring resistors Rx on column wiring 102 formed of conductors such as metal and wiring resistors Ry and Ryo on row wiring 103 formed of conductors such as metal can be mentioned. Since currents flows into the row wiring 103 from columns, the wiring resistors Ry and Ryo on the row wiring 103 in a panel 100 become predominant.
A method for compensating the voltage drop caused by the wiring resistors in the panel is disclosed in, for example, Japanese Patent Application Laid-Open (JP-A) No. 2002-221933.
Furthermore, conventionally a large area transistor having a large gate width is used as a switch in an output buffer 106 so as to make the voltage drop caused by on-resistance Ron of the switch in the output buffer 106 in a row drive circuit negligible. Therefore, the occupied area on a chip in the case where the row drive circuit is integrated onto one chip becomes large, and the IC chip becomes expensive.
Therefore, a method using a compensation circuit in which the voltage drop caused by the on-resistance is compensated by using a transistor that is smaller than the conventionally adopted one in the output buffer and feeding back a detected voltage at an output terminal 110 has been studied.
However, even this is not a compensation method that is sufficient for enhancing the precision of the drive. For example, a connection member 105 itself; such as flexible wiring, which connects a row drive circuit to the panel 100, has resistance Rfpc. It is demanded to compensate the voltage drop caused by the connection resistance Rfpc with a relatively simple configuration.
In the above-described compensation circuit in which the voltage drop caused by the on-resistance is compensated by feeding back the detected voltage at the output terminal, the detection terminal must be set on the emitting device side serving as the load as compared with the connection resistance Rfpc. Therefore, extra wiring paths become necessary and the arrangement pitch of conductor patterns of flexible wiring becomes high density, resulting in increased parasitic capacitance and a higher cost.